1. Field of the Invention
This invention relates to (meth)acrylic acid type polymers used advantageously for such applications as water type dispersants, descaling agents, and detergent builders, a method for the production thereof, and a detergent using thereof.
This invention also relates to unsaturated polyalkylene glycol type copolymers used advantageously for such applications as water type dispersants, descaling agents, cement additives, and detergent builders, a method for the production thereof, and detergents using thereof.
2. Description of the Related Art
<Prior Art Concerning (meth)acrylic Acid Type Polymer>
Of such water-soluble polymers as polyacrylic acid and polymaleic acid, those which have low molecular weights have been heretofore used advantageously for dispersants directed toward inorganic pigments and metal ions, descaling agents, and detergent builders. As a means for obtaining such water-soluble polymers of low molecular weights, the methods which are disclosed, for example, in JP-A-64-38403 and JP-A-05-86125 have been known.
The method disclosed in JP-A-64-38403, in radically polymerizing one or more water-soluble vinyl monomer (ethylenic monomer) with the use of a water-soluble azo type radical polymerization initiator, contemplates the presence in the reaction system of 0.1–30 mol % of sulfurous ion based on the quantity of the monomer. The monomer used in this case does not need to be particularly restricted but is only required to be a water-soluble vinyl monomer. The use of this method allows production of water-soluble polymers of low molecular weights not less than several tens of thousand with satisfactory reproducibility.
JP-A-05-86125 obtains a water-soluble polymer formed of not less than 95 mol % of acrylic acid or an acrylate by subjecting acrylic acid or an acrylate to aqueous solution polymerization while retaining the pH of the solution in the range of 6–9 (under the neutral condition). At this time, the number average molecular weight of the polymer is in the range of 300–10000 and the degree of dispersion is in the range of 1.3–2.3. Since the water-soluble polymer obtained by this method has a low molecular weight and has a degree of dispersion in a narrow range (having a narrow molecular weight distribution), it exhibits a high degree of dispersibility and is used advantageously for various dispersants and detergent builders.
JP-B-60-24806 discloses a method for producing an acrylate type low molecular weight polymer. The method of JP-B-60-24806 consists in subjecting (A) an alkali metal salt of acrylic acid, (B) acrylamide or 2-hydroxyethyl (meth)acrylate, and (C) a hydrophilic monomer capable of copolymerizing with the (A) and (B) components mentioned above in a prescribed ratio to aqueous solution polymerization. The polymerization conditions are not less than 10 liters of air per mol of the (A) component and a polymerization temperature of not higher than 80° C.
The acrylate type water-soluble polymer obtained by this method has a molecular weight in the range of 500–100000 and a narrow molecular weight distribution. Further, the water-soluble polymer entrains no impurity and incurs coloration only slightly. Moreover, the terminal of the straight chain or the side chain of this water-soluble polymer is capable of introducing 0.5–1.5 sulfonic groups per molecule. The water-soluble polymer, therefore, excels in dispersibility and the chelating property and can be advantageously used for dispersants directed to inorganic pigments, detergent builders, cleaning agents, and descaling agents.
As a technique for producing a low molecular polymer which is not such a water-soluble polymer as mentioned above, the method disclosed in U.S. Pat. No. 3,646,099 may be cited. The low molecular weight polymer which is disclosed in this publication is intended for use in electroconductive coating materials. It is formed by polymerizing (meth)acrylonitrile and a hydrophobic monomer and has to fulfill the essential requirement that the hydrophobic monomer be in a proportion of not less then 40 mol %. By this method, it is made possible to produce a polymer having a molecular weight of not more than 25000.
By the techniques disclosed in JP-A-64-38403 and JP-A-05-86125, however, it is difficult to introduce a sulfonic group quantitatively into the terminal or the main chain of the relevant polymer. The water-soluble polymers obtained by these techniques, therefore, hardly deserve to be rated fully excellent in the dispersibility and the anti-gelling property and are not optimum for dispersants, detergent builders, cleaning agents, and descaling agents.
By the technique which is disclosed in JP-B-60-24806, it is made possible to obtain a water-soluble polymer having a sulfonic group introduced to a certain degree therein. Since the monomer used in this technique is an acrylate (alkali metal salt), the system of polymerization reaction is substantially completely neutralized.
In the polymerization performed in such a neutral state as uses an acrylate, when the concentration of a solid component in the reaction system is heightened, the viscosity of the reaction solution tends to increase conspicuously in accordance as the polymerization proceeds and the molecular weight of the produced polymer tends to increase to a copious degree. Thus, the technique taught in JP-B-60-24806, when used in the polymerization of a monomer, is at a disadvantage in failing to produce a polymer of a low molecular weight under the condition of a high concentration and incurring a decline in the efficiency of production.
Further, by the technique disclosed in U.S. Pat. No. 3,646,099, it is made possible to produce a polymer of a low molecular weight advantageously. The technique disclosed in U.S. Pat. No. 3,646,099, however, is directed toward producing a polymer using a hydrophobic monomer in a proportion of not less than 40 mol %. The low molecular weight polymer consequently obtained is not soluble in water. Specifically, the technique disclosed in U.S. Pat. No. 3,646,099 is directed toward producing a low molecular weight polymer for use in electroconductive coating materials. By simply substituting the monomer for a water-soluble monomer, it is not possible to produce satisfactorily a water-soluble polymer.
In order for the water-soluble polymer of a low molecular weight mentioned above to be used advantageously for dispersants, descaling agents, and detergent builders, the water-soluble polymer is preferred to excel in the anti-gelling property, i.e. quality of rejecting gelation, besides the dispersibility and the Ca-binding capacity which are inherent in the water-soluble polymer. The techniques disclosed in the publications mentioned above, however, are incapable of producing a water-soluble polymer excelling in the anti-gelling property. They are, therefore, incapable of obtaining a water-soluble polymer possessing properties which fully befit dispersants, descaling agents, and detergent builders.
Thus, the methods described above are not fully satisfactory for the water-soluble polymer of a low molecular weight which excels in the dispersibility and the anti-chelating property and excels in the anti-gelling property as well and for the purpose of effecting efficient production of the water-soluble polymer.
The present inventors have discovered that a (meth)acrylic acid type polymer of a low molecular weight excelling in the dispersibility and the chelating property and in the anti-gelling property as well can be efficiently produced by polymerizing a monomer having a sulfonic group quantitatively introduced into the terminal and containing (meth)acrylic acid under an acidic condition. The (meth)acrylic acid type polymer mentioned above is a polymer which is formed by polymerizing 50–100 mol % of (meth)acrylic acid and 0–50 mol % of a water-soluble monoethylenically unsaturated monomer capable of copolymerizing with the (meth)acrylic acid in an aqueous solution and which has a sulfonic group linked to the terminal thereof. This (meth)acrylic acid type polymer is characterized by the fact that the value Q representing the anti-gelling ability defined by the formula, Q=Degree of gelation×105/weight average molecular weight, is less than 2.0. The (meth)acrylic acid type polymer is a water-soluble polymer of a low molecular weight which excels in the anti-gelling property and in the dispersibility and the chelating ability as well. In the method for the production of this polymer, the hydrophilic monomer containing not less than 50 mol % of (meth)acrylic acid is used in a proportion of not less than 60 mol %, the pH of the system used for polymerizing the monomer is less than 5, and the degree of neutralization is less than 40 mol %. The monomer mentioned above is polymerized by using as an initiator the combination of one or more species respectively of persulfate and bisulfite. More preferably, a hydrophilic monomer containing at least 50 mol % of (meth)acrylic acid is used in a proportion of not less than 60 mol % and, while this monomer is added dropwise to be polymerized under such acidic conditions as a pH of less than 5 and a degree of neutralization of less than 40 mol %, the solid concentration of the system of polymerization at the time that the dropwise addition of the monomer is completed is set at a level of not less than 40 mass % and the weight average molecular weight is set at a level in the range of 3000–15000. The present inventors have found that in consequence of the polymerization, a water-soluble polymer of a low molecular weight excelling in the anti-gelling property and in the dispersibility and the chelating ability can be produced with high efficiency. This knowledge has been proposed in JP-A-11-315115.
The water-soluble polymer of JP-A-11-315115 has been finding extensive utility because it is possessed of properties befitting dispersants, descaling agent, and detergent builders.
<Prior Art Concerning Unsaturated Polyalkylene Glycol Type Copolymer>
It has been known that copolymers formed by using an unsaturated polyalkylene glycol type monomer are useful as builders for liquid detergents. For example, the copolymers of such unsaturated polyalkylene glycol type monomers as ethylene oxide adducts of 3-methy-3-buten-1-ol and such unsaturated monocarboxylic acid type monomers as (meth)acrylic acid are useful as liquid detergent builders. As a means to obtain such a copolymer, the method disclosed in JP-A-2002-60785, for example, has been known.
The method disclosed in the publication mentioned above, in copolymerizing a monomer component essentially containing either an unsaturated monocarboxylic acid type monomer or an unsaturated dicarboxylic acid type monomer and an unsaturated polyalkylene glycol type monomer, effects the necessary polymerization by using a persulfate or hydrogen peroxide as an initiator. When this method is used, a copolymer having a molecular weight up to several tens of thousand can be obtained with high reproducibility.
The polymer which is obtained by this method excels in the compatibility with a liquid detergent and in the dispersibility and can be advantageously used for detergent builders, particularly liquid detergent builders.
As a technique for producing a (meth)acrylic acid type polymer of a low molecular weight, which is not a polymer containing an unsaturated polyalkylene glycol type monomer, the method disclosed in JP-A-11-315115 may be cited.
By the method disclosed in the publication mentioned above, when a monomer component essentially containing a (meth)acrylic acid type monomer is polymerized, the polymerization is effected at a high concentration of not less than 40 mass % by using a persulfate or a bisulfite as an initiator. By using this method, it is made possible to obtain a low molecular weight polymer having a molecular weight of not more than several tens of thousand with high reproducibility.
The polymer which is obtained by this method has a narrow molecular weight distribution and incurs coloration only slightly. Further, this polymer has sulfur oxygen acid quantitatively introduced into the terminal of the straight chain or to the side chain thereof. Thus, this polymer excels in the dispersibility and the anti-gelling property and can be advantageously used for dispersants directed toward inorganic pigments, detergent builders, cleaning agents, and descaling agents.
When a copolymer of a (meth)acrylic acid monomer and an unsaturated polyalkylene glycol type monomer is produced by using the technique disclosed in JP-A-2002-60785, however, the polymer has the molecular weight thereof increase unless the polymerization concentration is lowered to the order of 20 mass %. The polymerization solution possibly succumbs to gelation. Thus, the polymerization concentration must be lowered at a sacrifice of productivity. Further, the aqueous solution of polymer consequently obtained has an inferior hue. In the light of these factors, the polymer does not deserve to be rated as optimum for detergent builders.
Further, by using the technique disclosed in JP-A-11-315115, it is made possible to produce a polymer of a low molecular weight in a high concentration. Since this technique is directed toward producing a polymer by mainly using a (meth)acrylic acid type monomer, the polymer obtained by the technique has low compatibility with liquid detergents. By the technique disclosed in JP-A-11-315115, therefore, it is difficult to produce a polymer suitable for liquid detergent builders.
By such conventional techniques as these, it has never been made possible to produce a polymer of a low molecular weight excelling in hue, compatibility with liquid detergents, dispersibility, and anti-gelling property at a high concentration with satisfactory efficiency.
<Problems Concerning (meth)acrylic Acid Type Polymer>
The present inventors, not satisfied with the development of this novel technique, have further continued a study concerning the (meth)acrylic acid type polymer and the method for production thereof disclosed in JP-A-11-315115 It has been consequently ascertained {circle around (1)} that the bisulfite used as an initiator emits sulfur dioxide in a large quantity during the course of the production, the generated sulfur dioxide dissolves in the liquid phase and forms an impurity, the sulfur dioxide which has escaped solution in the liquid phase is discharged from the system in a large quantity, and the discharged sulfur dioxide gives rise to a new problem of necessitating a costly treatment which comprises recovering this harmful gas with a proper adsorbent and discarding the spent adsorbent and {circle around (2)} that since the bisulfite as an initiator escapes in the form of sulfur dioxide and incurs loss of effect, the molecular weight of the polymer is not lowered, the total quantity of the initiator required is increased, the production is suffered to form a large quantity of an impurity, the high performance owned inherently by the produced (meth)acrylic acid type polymer is not manifested fully satisfactorily, and a new problem of degrading quality and inducing precipitation of an impurity during the preservation at a low temperature is encountered.
An object of this invention, therefore, is to provide a (meth)acrylic acid type polymer which is a water-soluble polymer of a low molecular weight excelling in dispersibility, chelating ability, and anti-gelling property. The (meth)acrylic acid type polymer of this invention has a prominently allayed impurity content and a further enhanced performance. Further, the (meth)acrylic acid type polymer of this invention possesses an outstanding ability to preserve constantly stably the high performance endowed during the course of production without being affected by the environment of preservation and suffers neither from degradation of quality nor precipitation of an impurity during the preservation at a low temperature.
Another object of this invention is to provide a method for producing a (meth)acrylic acid type polymer which is a water-soluble polymer of a low molecular weight excelling in dispersibility, chelating ability, and anti-gelling property. By the method of this invention for the production of a (meth)acrylic acid type polymer, it is made possible to produce a (meth)acrylic acid type polymer which allays generation of a large quantity of sulfur dioxide and generation of an impurity and acquires a further enhanced performance.
Still another object of this invention is to provide a detergent formed by using (as a high performance detergent builder) a (meth)acrylic acid type polymer which is a water-soluble polymer of a low molecular weight excelling in dispersibility, chelating ability, and anti-gelling property. The detergent of this invention acquires a further enhancement of performance and quality. Further, the detergent of this invention is possessed of a high ability of effecting stable preservation incapable of being effected by the environment of preservation.
<Problems Concerning Unsaturated Polyalkylene Glycol Type Copolymer>
The unsaturated polyalkylene glycol type copolymer disclosed in JP-A-2002-60785 indeed excels in compatibility with liquid detergents and dispersibility and nevertheless betrays deficiency in hue and in productivity as well. Meanwhile, the polymer disclosed in JP-A-11-315115 is deficient in compatibility with liquid detergents. The problem to be fulfilled by this invention, therefore, resides in providing a liquid detergent grade builder, a cement additive, and a detergent containing the liquid detergent grade builder which excels in compatibility with liquid detergents, dispersibility, and hue.
Further, the object to be fulfilled by this invention consists in providing a method for polymerizing an unsaturated polyalkylene glycol type copolymer excelling incompatibility with liquid detergents, dispersibility, and hue in a high concentration with high productivity.